AbstractChlorinated phenols (CPs), including pentachlorophenol, selected positional isomers from each major group of CPs, and phenol were previously selected from 38 possible compounds and ranked according to developmental toxicity. The present study was designed to utilize these compounds (and a variety of chemical derivatives) to elucidate the mechanism(s) of developmental toxicity of the chlorinated phenols. Mitochondria were isolated by differential centrifugation from rat embryos (REM) and maternal liver (MLM) on day 15 of gestation. The higher CPs, i.e., pentachlorophenol (C5P), 2,3,4,5‐tetrachlorophenol (2,3,4,5‐C4P), and 2,3,5‐trichlorophenol (2,3,5‐C3P) at concentrations>1.33 μM, inhibited ADP phosphorylation and state 4 respiration in the presence of either glutamate plus malate or α‐ketoglutarate or succinate. These compounds also exerted a significant uncoupling activity at a concentration of 1.33 μM, with C5P>2,3,4,5‐C4P>2,3,5‐C3P. The lower CPs, i.e., 3,5‐dichlorophenol (3,5‐C2P), 4‐chlorophenol (4‐CP), and phenol, produced comparable mitochondrial effects, but only at a higher concentration (20 μM). Enhanced mitochondrial ATPase activity (with and without Mg2+) was induced by C5P, 2,3,4,5‐C4P and 2,3,5‐C3P at concentrations that exhibited maximum uncoupling activity. The CPs (except for the derivative C5P‐anisole) caused significant mitochondrial swelling. The reversal of oligomycin‐inhibited respiration by C5P from REM or MLM was also reproducible in the intactHydra attenuata. A correlation of 0.9 (p= 0.0151) between CP‐induced uncoupling activity and the reciprocal of the minimal affective concentration in theHydradevelopmental assay was observed. These findings suggest that CPs may elicit their effects by intera
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